The invention relates to a dental unit according to preamble of the following patent claim 1 and a method according to preamble of the following patent claim 14 for feeding water to instruments of a dental unit and/or to other water outlet points of a dental unit.
In dental units there is typically used as feed water either water treated separately outside the system or the unit is connected to a public water system. With respect to the latter, orders of the authorities in numerous countries specify various criteria e.g. in relation to how connection to the water system needs to be arranged in order to prevent water that may get contaminated at the point of use flowing backwards to the water system. One such order of the authorities requires arranging a reservoir basin open to atmospheric pressure and the feed link of the water system at a distance from each other, i.e. in practise, physical separation of the feed water line of a dental unit from the water system.
According to typical prior art technology, uncontrolled pressure alterations in the water lines is a problem of many of the feed water arrangements of dental units, which can cause leakages in valves or gaskets, annoying splattering at the water outlet points of the dental unit, breaking of the pressure sensors and in some cases even hampering operation of the dental instruments. Special attention must be paid to controlling the pressure of the feed water line when the public water system is used as the water source but the feed water line is physically separated from the water system, e.g. due to the orders of the authorities as discussed above, in which case the relatively stable pressure typical for a public water system cannot be taken advantage of. Such a basic solution has been described e.g. in a U.S. Pat. No. 5,039,405, and one such kind of an application for re-pressurizing the feed water in an EP patent publication 0 524 344 B2, having been granted in modified form after an appeal. With a solution according to that EP patent, i.e. parallel use of two pumps of a specific construction, it is possible to keep pressure of the instrument water lines fairly stable, but with respect to automatic control engineering the arrangement is somewhat complicated and also comprises of quite a number of moving parts.